package com.gyj.Test.LinkedList;

/**
 * Created by Gao on 2018/4/4.
 */
public class MergeTwoSortedList {

    public class ListNode {
        int val;
        ListNode next = null;

        ListNode(int val) {
            this.val = val;
        }
    }

    /**
     * 递归
     * @param list1
     * @param list2
     * @return
     */
    public ListNode Merge(ListNode list1, ListNode list2) {

        if (list1 == null) {
            return list2;
        }
        if (list2 == null) {
            return list1;
        }

        ListNode pMergeHead = null;
        if (list1.val < list2.val) {
            pMergeHead = list1;
            pMergeHead.next = Merge(list1.next, list2);
        } else {
            pMergeHead = list2;
            pMergeHead.next = Merge(list1, list2.next);
        }

        return pMergeHead;
    }


    /**
     * 非递归
     * @param list1
     * @param list2
     * @return
     */
    public ListNode Merge1(ListNode list1, ListNode list2) {
        if (list1 == null) {
            return list2;
        }
        if (list2 == null) {
            return list1;
        }
        ListNode mergeHead = null;
        ListNode current = null;
        while (list1 != null && list2 != null) {
            if (list1.val <= list2.val) {
                if (mergeHead == null) {
                    mergeHead = current = list1;
                } else {
                    current.next = list1;
                    current = current.next;
                }
                list1 = list1.next;
            } else {
                if (mergeHead == null) {
                    mergeHead = current = list2;
                } else {
                    current.next = list2;
                    current = current.next;
                }
                list2 = list2.next;
            }
        }
        if (list1 == null) {
            current.next = list2;
        } else {
            current.next = list1;
        }

        return mergeHead;
    }

}
